This invention relates to a hydrocarbon conversion process and more particularly to a process and catalyst for the isomerization of isomerizable hydrocarbons. Pursuant to this invention, a commercially useful process for the hydroisomerization of C.sub.4 to C.sub.6 paraffins is provided together with an improved catalyst and method of making the same.
It is known that normal paraffins having four to six carbon atoms may be isomerized to their branched chain isomers by employing chlorided metal-alumina catalysts. Isomerization catalysts of this type are typically prepared by activating a metal-alumina composite with a chloride activating agent or combination of agents as described in U.S. Pat. Nos. 3,551,516, 3,555,107 and 3,567,796, all assigned to the assignee hereof. Accordingly, isomerization catalysts can be prepared by chloriding composites of metal and alumina where the metal can be, for example, platinum, palladium, rhodium or ruthenium. The composite is contacted with, for example, a chloroalkane or an acid chloride or other chloriding system known to the art under conditions enabling the activating agent to react with the metal-alumina composite and resulting in the preparation of catalysts having a chlorine content of about 3.0 to 15.0 weight percent. The chlorided catalyst can thereafter be stabilized pursuant to the description and procedure set forth in U.S. Pat. Nos. 3,440,300 and 3,440,301.
While the procedures heretofore employed enabled the preparation of active catalysts and the isomerization of normal paraffins in the presence thereof, problems not heretofore apparent were encountered in scaling the process to commercial size operations. More specifically, in the course of preparing the catalyst by chloriding substantial amounts of metal-alumina composite, more than the stoichiometric amount of activating agent is needed so as to chloride the composite to a level of 3.0 to 15.0, typically 4.0 to 8.0, weight percent. While the use of excess activating agent produced no apparent deleterious affects when relatively small or laboratory amounts of catalyst were prepared, such is not the case when substantial amounts of catalyst are needed for commercial size operations. It has been found that the use of more than stoichiometric amounts of activating agent in commercial size operations can effect loss of metal from the composite leading to a catalyst having lower catalytic activity and an isomerization process providing less converted normal paraffins to isoparaffins. Inasmuch as the metal of choice of the isomerization catalyst is generally platinum, substantial loss of platinum from the catalyst produces severe economic penalties in terms of the cost of the catalyst and the isomerization process employing the same.
Further, the loss of metal from the catalyst can result in catalyst beds having uneven distributions of metal. For example, where an in-situ activation procedure is employed as when a bed of metal-alumina composite is contacted with a flowing stream of chloride activator, the portion of the catalyst first contacted by the stream can undergo metal depletion. As a consequence the metal content of this portion of the bed can be substantially less than that of the bed later contacted by the stream. While reduction in the amount of chloride activator employed can reduce the metal losses from the initial portion of the bed, the latter portion may undergo a somewhat lesser degree of activation in that less chloriding agent is available when contacting occurs. Further, since some channeling in the bed may occur in the course of activation, reduced amounts of activator increase the opportunity for portions of the bed not to be contacted with activating agent thereby resulting in either inactivated or poorly activated catalyst portions.
Moreover, metal-alumina composites represent materials commercially available from various sources. While the chemical compositions of the commercial or otherwise prepared composites are generally uniform or similar, the properties with respect to the composites' ability to retain metal during activation may nevertheless vary. For example, in one instance substantial amounts of metal may be depleted from the composite when contacted with the activating agent whereas another commercial lot may be more resistant to depletion of the metal. Accordingly, the known procedures for providing an activating catalyst are also dependent upon the metal-alumina composite which in turn may necessitate numerous and costly alterations in the activation procedure. A uniform method capable of preparing isomerization catalysts from composites varying in properties has not heretofore been available.
It is therefore an object of this invention to provide a process for the hydroisomerization of paraffinic hydrocarbons employing an improved catalyst composed of a noble metal, alumina and chlorine.
Another object of this invention is to provide a method for the preparation of an isomerization catalyst of high activity where the amount of metal retained on the catalyst's surface during activation is maximized.
Yet another object of this invention is to provide a method for the in situ activation of an isomerization catalyst where the loss of metal from the composite upon activation is deterred.
Other objects and advantages of this invention will become apparent from the following detailed description of the invention.